大毘盧遮那成佛經疏 13.89

13.89

次如來念處印。作三補吒（此皆如未剖之蓮，極空中合掌也。更撿前文勿令錯也）以二空二風聚相捻，即是也。其捻法，當令四个指指甲相到耳。真言歸命如前。

Next is the mudrā of the Tathāgata's Applications of Mindfulness (smṛtyupasthāna). Form the saṃpuṭa (all of these are like an unopened lotus, with hollowed palms joined; check the earlier text again so as not to make an error), gather the two space [thumbs] and two wind [index fingers] together to pinch each other, and this is it. The method of pinching is that the nails of the four fingers should meet each other. The mantra homage is as before.